Corrosion inhibitors are compounds or formulations of chemical compounds wherein the active part blocks or modifies the electronic transfer process, responsible of the corrosion phenomena, between the metallic surface and the surrounding medium. In the petroleum industry, its use is generalized to control metal corrosion in a wide variety of mediums and conditions. Independently of the system, the interaction between the active component and the metallic surface plays a determining role in its development and consequently in the corrosion control; said interaction depends on the chemical properties of the active compound depending on its molecular structure, on physical and chemical properties of the metal and its own interaction with the surrounding medium; furthermore, of the operation conditions such as system pressure, temperature and hydrodynamics.
In the particular case of pipes for the transportation of crude oil (pipelines), the control of the internal corrosion is complicated mainly by the frequent variations present in the type of the transported crude, as well as in the water, salts and dissolved gases contents; nevertheless, the use of inhibitors is still the more profitable alternative to face it.
Among the main chemical families that have been used to inhibit corrosion in pipelines are nitrogenous compounds such as ammonium quaternary salts, amines, amides and including amino acids; particularly the use of fat imidazolines and fat amines as corrosion inhibitors in the petroleum industry is well known. Generally, it is accepted that these compounds work upon absorption forming a protecting film over the metallic surface; nevertheless, independent of the inhibitor used, these also have limitations.
In the literature that mentions the use of corrosion inhibitors with specific application for hydrocarbons transport, are the following international patents:
U.S. Pat. No. 7,057,050 refers to the preparation of novel corrosion inhibitors imidazoline base and its use to inhibit corrosion in metallic flow lines. According to the patent, the inhibitors are a series of new corrosion inhibitors based on imidazoline base substituted with acrylates, of the following formula:

Wherein R1 is an alkyl radical having from 2 to 8 carbon atoms; R2 is a radical derived from a fatty acid, and R3 is a radical derived from an unsaturated acid.
U.S. Pat. No. 7,160,507 relates to an additive and a method of corrosion inhibition on devices used for the recovery, transportation and processing of crude oil; the inhibitor comprises an alkoxylated quaternary compound of the formula:

where R1 and R2 are independently groups of the formula —(B)—(O-A)n-O—CO—R5 or -(A-O)n—(C)—CO—O—R5; R3 is C1- to C30-alkyl or C2 to C30-alkenyl; R4 is an organic radical with 1 to 100 atoms optionally containing heteroatoms; R5 is an alkyl or an alkenyl; n is a number from 1 to 20; A is an alkylene group; B is an alkylene group, C is a C1- to C30-alkylene and X is an anion.
In patent application U.S. Pat. No. 0,084,612 A1, a method for inhibiting corrosion in metallic surfaces used in manufacture, transportation, storage and separation of crude oil and gas is described; the method comprises adding the fluid a sufficient quantity of a synergist, when H2S is present in the fluid, or no synergist when H2S is present in the fluid and a composition comprising the following formula and salts thereof:

Wherein R1 and R3, CnH2n+1 wherein n=0 to 12; benzyl; or H. R2 is a C1 to C22 alkyl. X— is a halogen or a carboxylate and is only present when R1 and R3 are present. Y is (CH2)n with n=1 to 8 and wherein R3 and R1 cannot be hydrogen at the same time.
Another structure mentioned in this patent application is:

wherein R1 and R2 are similar to the above structure and is CnH2n+1 wherein n=0 is a C1 to C22 alkyl. X—═Cl, Br or I.
WO 157234 relates to novel quaternary-nitrogen compounds in its structure and formulations used by these compounds that are useful as corrosion inhibitors in the gas and petroleum industry. The quaternary nitrogen-containing corrosion inhibitors have the following formula:

Wherein:
is an aromatic, nitrogen-containing ring of 5 to 14 atoms, optionally containing an additional N, O or S ring atom in the additional N ring or can be substituted with one or more alkyl, alkenyl, aryl, arylalkyl, cycloalkyl, amine, aminoalkyl, alkoxy, hydroxyalkyl or cyano groups, or a mixture thereof; Y is a group of formula —OC(O)R1; L is an C1-C10 alkyl, C2-C20 alkenyl of the formula —CH2CH(OR2)CH2—; R1 is C8-C20 alkenyl; R2 is H or —C(O)R1; R3 and R4 are independently selected from H, alkyl, alkenyl, amino, aminoalkyl, alkoxy, hydroxyalkyl or cyano; and X is Br, Cl or I.
WO 091429 relates to corrosion inhibition in ferrous and non-ferrous metals in aqueous-based environments by the use of formulations that use at least two mercaptan compounds of the following formulae:

wherein X is C, N, O or S; R1, R2, R3 y R4 are independently H or methyl; n and m are independently integers from 1 to 5 and p and q are independently integers from 1 to 4.

wherein m is an integer from 3 to 4; and

wherein m is an integer from 1 to 4; and n=4−m.
WO 128313 relates to a corrosion inhibitor for use in the oil and gas exploration, recovery and processing industries consisting of a quaternary ammonium compound of the formula:

wherein R is C1-6 alkyl, C2-6 alkenyl, aryl, arylalkyl; X, Y and Z are each independently H or R1CO— group, provided that at least one of X, Y, Z is R1CO— where R1 is a C5-23 alkyl or alkenyl containing 0, 1, 2, or 3 double bounds; D is C2-6 alkylene; E is C2-4 alkylene; p, q and r are independently integers from 0 to 20, with the proviso that p+q+r=3 to 20; and A is an anion.
Other patent applications related to corrosion inhibitors with application in crude oil transportation are patent application WO 000895 that refers to a polymeric product obtained by the reaction between alkoxylated fat amine and a dicarboxylic acid derivative, whereas patent application WO 028542 refers to the use of polyamine polyester compounds and polyquaternary polyester ammonium as corrosion inhibitors in the transportation of crude oil and in the oil and gas wells.